Implement a .clean method for the WorkflowAction class.

Pass the view request to the form so that it can be passed to the
WorkflowAction clean method.

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

mayan/apps/document_states/classes.py

@@ -44,6 +44,10 @@ class WorkflowActionBase(object):
 
 
 class WorkflowAction(six.with_metaclass(WorkflowActionMetaclass, WorkflowActionBase)):
+    @classmethod
+    def clean(cls, request, form_data=None):
+        return form_data
+
     @classmethod
     def get(cls, name):
         return cls._registry[name]